Clinical validation of CTC subtype frequency to prognosis OS in mCRPC patients.

Abstract

302 Background: CellSearch is an FDA cleared assay that enumerates intact CK+, DAPI+, CD45- cells via EpCAM capture. CTC number is prognostic for survival pre- and post- systemic therapy. These cells are a subset of confirmed genomically altered CTC’s in blood. We report the prognostic significance for OS in mCRPC of CTC subtypes not enumerated by CellSearch including apoptotic CTCs, CK- CTCs, small CTCs, and CTC clusters. Methods: 221 blood samples from 179 unique patients were collected from pts about to begin AR directed (n = 150) or taxane (n = 71) therapy for progressive CRPC. Samples were analyzed utilizing the Epic Sciences platform to enumerate traditional (CK+, abnormal morph), apoptotic (CK+, fragmented nuclei), CK- (CK-/abnormal morph), small (CK+, normal morph), and CTC clusters. Patients were followed for up to 2.3 yrs. Paired CellSearch and Epic traditional CTC counts were collected on 173 patient samples. Results: In paired analysis, Epic traditional CTCs were identified in 86% of patients vs. 67% by CellSearch, and any Epic CTC subtype was found in 96% of the patient samples. Increased frequency of any CTC subtype was a univariate predictor of OS (see table). Conclusions: Epic identified CTC subtypes not identified by CellSearch or other technologies that select or sort based upon size or epithelial expression. Cells were detected in 96% of the patient samples and all 5 subtypes were found to be prognostic for survival. The biologic characterization of CTC subtypes as a biomarker of drug sensitivity is ongoing. The increased clinical sensitivity of subtypes and prevalence of CTCs identified on the Epic platform provides a greatly expanded array of clinically relevant biomarkers to develop predictive liquid biopsy signatures in the metastatic setting. [Table: see text]